From https://bugs.launchpad.net/catfish-search/+bug/1769572 Validating catfish.appdata.xml using appstream-util fails like below: $ appstream-util validate-relax --nonet ./catfish-1.4.5/_TMPINSTDIR/python2/usr/share/metainfo/catfish.appdata.xml ./catfish-1.4.5/_TMPINSTDIR/python2/usr/share/metainfo/catfish.appdata.xml: FAILED: • attribute-invalid : <release> timestamp is in the future Validation of files failed This is because the file data/metainfo/catfish.appdata.xml.in has entry: 96 <release version="1.2.0" date="2018-08-16"> ... which is newer than 89 <release version="1.2.1" date="2014-08-19"> Perhaps the release date for 1.2.0 should be 2014-08-16.
Sean Davis referenced this bugreport in commit 46593ce5d2f07345fd423bbe59ea8b8d0d8d14a3 Fix invalid date in appdata (bug #14502) https://git.xfce.org/apps/catfish/commit?id=46593ce5d2f07345fd423bbe59ea8b8d0d8d14a3
Fixed in the above commit.